Edward Snowden's lawyer has told Sky News the latest spy row between Berlin and Washington centres on claims the CIA snooped on a German investigation into earlier US eavesdropping.

The German government ordered the American spy agency's chief in Berlin out of the country on Thursday.

The diplomatic crisis between the two allies comes as German authorities pursue investigations against two officials suspected of spying for the US.

Snowden's lawyer says US-German ties are at their lowest since WW2

Jesselyn Radack, who represents Mr Snowden, said the row is rooted in the fugitive intelligence contractor's disclosures last year that the US National Security Agency (NSA) had snooped on German Chancellor Angela Merkel's mobile phone.

Those claims prompted the German government to launch an investigation, which the American intelligence services have been spying on, according to Ms Radack.

She told Sky News: "This was a CIA mole that was spying on the Bundestag's investigation into NSA spying on German people. It is outrageous.

"And it's also stunning to me that the US would interfere with another country's democratic political process. It would be like having a spy spying on Congress.

"It makes you wonder what more the US has to hide if it's going to such lengths to thwart the investigation that the Bundestag has into the NSA.

"This spy scandal is the biggest such eruption since World War Two."

German officials confirmed earlier that the top US spy at the American embassy had been asked to leave the country.

Government spokesman Steffen Seibert said: "The request occurred against the backdrop of the ongoing investigation by federal prosecutors as well as the questions that were posed months ago about the activities of US intelligence agencies in Germany.

"The government takes the matter very seriously."

Clemens Binninger, head of a parliamentary oversight committee on intelligence, said the move was "a reaction to the long-lacking co-operation in efforts to get to the bottom of this affair".

White House Press Secretary Josh Earnest did not directly comment about the matter other than to say the US-German national security relationship was important.

Shortly before the expulsion was announced, Ms Merkel told reporters that trust was essential in any partnership.

"If what we hear right now is true," she said, "I have to say that from my point of view, spying on allies is a waste of energy in the end."

News website Spiegel Online said the expulsion was a "diplomatic earthquake", usually reserved for "pariah states" such as North Korea.

The latest row stems from the arrest last week of a 31-year-old German intelligence agency employee on suspicion of selling more than 200 documents to the CIA.

Then on Wednesday police searched the Berlin-area home and office of a German defence ministry official who local media report is also suspected of spying for the US.